Volumetric Modulated Arc Therapy (VMAT)
Rotational IMRT delivered during continuous gantry rotation with simultaneously modulated MLC leaves, dose rate, and gantry speed. Delivers conformal dose distributions in 2–6 minutes per fraction — roughly a third to a fifth of conventional step-and-shoot IMRT time. Now the dominant external beam technique for head/neck, prostate, pelvis, and many other sites.
Clinical pathway
- CT simulation with immobilization (mask, Vac-Lok, prone breast board, etc.) and IV contrast as indicated.
- Contouring — GTV, CTV, PTV, OARs; often fused with MRI or PET.
- Inverse planning — VMAT optimization (Eclipse, RayStation, Monaco) with 1–4 arcs, partial or full.
- Plan review + QA — patient-specific IMRT QA (portal dosimetry, ArcCheck, Delta4) before first fraction.
- Daily treatment — kV-kV or CBCT image guidance, couch shift, delivery.
Typical systems
- Varian TrueBeam family
- Elekta Versa HD
- Elekta Infinity
- Accuray Radixact (helical IMRT, adjacent technique)
Room + procedure characteristics
- Delivery time: 2–6 min per fraction
- Dose rate: typically 600 MU/min, some FFF plans at 1200–2400
- QA: TG-142 daily, monthly, annual; patient-specific IMRT QA before each plan